1. Field of the Invention
This invention relates to a semiconductor integrated circuit device, particularly to a semiconductor integrated circuit device wherein chips due to such a master slice that a plurality of basic cells are regularly placed on a semiconductor substrate are used and a plurality of macrocell functional blocks which were previously prepared are formed in combination with each other on said chips so as to fulfill a prescribed function.
2. Description of the Prior Art
In a semiconductor integrated circuit device made according to a master slice method, a chip of a master wafer, i.e. a master chip, on which basic cells are regularly placed is provided. A logic design is worked out using macrocells, i.e. macros, which are previously designed and registered in a library. Wirings are performed on the master chip according to the design so as to realize a necessary logic and memory function on said chip.
The term "macro" means the cell which has a number of functions, many elements and large area. According to the size of the macro, it is referred to as a large scale, middle scale or small scale macro.
According to the above master slice method, it is possible to accomplish a product within a short time after receipt of a user's request and to supply at a relatively low price a product according to a diversified small-quantity production.
In the above-mentioned semiconductor integrated circuit device, integrated density is yearly improved. A logic circuit which can be constructed on one semiconductor integrated circuit tends to become large. Consequently, it has become possible for one semiconductor integrated circuit device to gather a circuit of such a scale that previously a design had to be worked out distributing it into a plurality of semiconductor integrated circuit devices. With regard to macros to be registered in the library, it has become necessary for such a large scale circuit that a design has been worked out as one semiconductor integrated circuit is treated as one macro. Such large scale macro includes, for example, a RAM, ROM, microprocessor and the like.
When the integrated circuit device could be constructed only by small scale macros, wirings between the macros were enough. Wirings between the adjacent macros and wirings jumping over the macros were not necessary. However, if the large scale macro, as mentioned above, is placed in the semiconductor integrated circuit device, signal wirings between the other macros and those between the macros and input-output buffers must be made on the large scale macro.
As a result, the wiring length becomes longer and a large parasitic capacitance is caused between the wiring layer and semiconductor element, thus high speed operation of the circuit is prevented. In addition, the logic design is subject to restriction on the aspect of fan in and fan out. Namely, for an output of some functional block, restrictions are generally put on output loading with reference to an index referred to as a fan out factor according to driving capability, but the logic design must be worked out by adding to this factor the load of parasitic capacitance due to the wirings. In the case that the parasitic capacitance is great, therefore, restrictions on the output loading become great and a free design is prevented.